The Anatomy of the Median Nerve

The Source of Carpal Tunnel Syndrome

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The median nerve is one of the major nerves supplying the upper extremity of the body. Beginning in the shoulder at the confluence of several branches of the brachial plexus, the median nerve travels down the upper extremity with branches extending all the way to the tips of the fingers. This nerve supplies information about sensations in the hand and provides information to muscles about when to contract.

Injuries to the median nerve can lead to common symptoms of pain, numbness, tingling, and weakness in the upper extremity. The most common condition of median nerve dysfunction is called carpal tunnel syndrome, a problem that occurs when the median nerve is compressed as it passes by the wrist joint.

Anatomy

A nerve is a structure within your body that can deliver information to and from the brain. Impulses are channeled along the pathway of a nerve from the central nervous system, consisting of the brain and spinal cord, to the organs of your body. Peripheral nerves travel throughout the body and serve as a connection among all of the bodily structures including organs, muscles, and skin to the central nervous system.

The median nerve is an important pathway that provides information about sensations to the brain and delivers messages to the muscles about when to contract.

The median nerve is formed in the shoulder at the level of the collarbone by the confluence of several branches of nerves coming from the spinal cord. This part of the nervous system is called the brachial plexus and forms the major nerves that supply the entire upper extremity.

The median nerve is one of these large nerves that travels from the shoulder down the arm, past the elbow joint, into the forearm, and ultimately across the wrist and into the hand. Other nerves that function similarly in the upper extremity include the ulnar nerve and the radial nerve.

Function

The median nerve has two critical functions. The first is to provide information about sensations from a specific location in the hand back to the brain. The second major function is to provide information from the brain to be delivered to muscles of the forearm and hand telling them to contract.

Sensation

The median nerve provides sensation to the skin of the palm side of the hand. The thumb, index, and long fingers each have their sensation provided by the median nerve. In addition, half of the ring finger also gets its sensation from the median nerve. This specific area of sensation is highly reproducible and is the reason why your physician will carefully assess the specific location of abnormal sensations.

If other parts of your hand are affected by abnormal sensations, it is likely that the culprit causing the altered sensation is not isolated to the median nerve. When assessing the sensation in your hand, your physician may test different types of sensation including two-point discrimination and pressure testing. A good examination of sensation can help determine the location and type of nerve damage that has occurred.

Motor Function

The median nerve provides motor function to most all of the flexor and pronator muscles of the forearm. These are the muscles used to perform a gripping motion such as making a fist, as well as those muscles that rotate your palm downward. By performing a careful examination, your physician can specifically assess each of these muscles.

In the hand, the median nerve provides motor function to the muscles at the base of the thumb (the thenar muscles) as well as the lumbrical muscles of the index and long fingers.

Your examiner may perform specific tasks to evaluate the strength of these muscles. In addition, chronic damage to the median nerve may be seen as atrophy or wasting of these muscles. In people with the condition carpal tunnel syndrome, a common sign of this problem is atrophy of the thenar musculature, the soft area of the palm directly underneath the thumb.

People who develop atrophy of these muscles from chronic carpal tunnel syndrome may have a loss of this normal soft tissue which can be seen when comparing the hands side by side.

Associated Conditions

By far, the most common condition associated with abnormal median nerve function is carpal tunnel syndrome. When the median nerve is compressed within the carpal canal, a typical set of symptoms will occur. However, median nerve abnormalities can occur as a result of abnormal nerve function at other locations in the upper extremity.

Other causes of median nerve damage include direct lacerations from penetrating injuries, injuries from fractures to the arm and forearm, and compression from external sources such as casts or splints.

Carpal Tunnel Syndrome

Carpal tunnel syndrome is a specific condition that is caused by compression of the median nerve as it passes through the carpal canal at the level of the wrist joint. The carpal canal is formed by the small bones of the wrist on one side and a ligament called the transverse carpal ligament on the other side. Within this canal are the tendons of the fingers as well as the median nerve. Typically, there is sufficient room within the carpal canal for the median nerve to function normally.

In people with carpal tunnel syndrome, however, the median nerve becomes pinched within this canal and nerve function becomes altered.

Since the canal walls (the bones of the wrist and the transverse carpal ligament) are rigid structures, there is a limited ability for your body to adapt and allow for more space within the canal. Chronic inflammation, systemic conditions (such as diabetes or hypothyroidism), obesity, pregnancy, and other conditions can all cause increased pressure within the carpal canal. When this pressure increases sufficiently, the nerve will begin to function abnormally.

People with carpal tunnel syndrome typically experience symptoms of numbness and tingling within the hands and fingers. Symptoms are often worse when holding the hands in a certain position such as holding a book or driving a car, and they are often worse at night. People with carpal tunnel syndrome often find they shake their hands to try and relieve the tingling and numbness in their fingers. Specific tests can be performed to assess median nerve function at the carpal canal, and this condition can typically be diagnosed by a skilled examiner.

If there is question about the underlying cause, a specific nerve test can be used to help determine if there is abnormal functioning of the median nerve within the carpal canal. Treatment can range from simple steps to alleviate pressure on the nerve, to surgical treatment to create more room within the carpal canal so the median nerve will begin to function normally.

Nerve Lacerations

Direct injuries to the nerve can be caused by a variety of penetrating injuries. Common types of penetrating injuries include stab wounds and broken glass injuries. Typically the location of a nerve laceration is readily apparent from the location of the skin injury. However, confirming the location by examining the function of the median nerve will help to confirm the suspected diagnosis. If a nerve injury is identified soon after the injury, often a direct repair of the nerve can be performed.

Injuries that are more widespread or long-standing may require nerve grafting to repair a damaged segment of the nerve. Healing of nerve injuries is notoriously slow and often leads to some level of permanent dysfunction. Healing of nerve injuries is largely related to the age of the injured individual. Younger children have a much better capacity to heal nerve injuries than adults.

Fractures

Specific fractures of the arm and forearm are often associated with nerve injuries. When a bone injury occurs, an associated nerve injury should be suspected. Your physician can examine the function of the nerves of the upper extremity to determine if there was any damage that occurred and if anything further needs to be done to prevent ongoing nerve problems.

Types of fractures commonly associated with median nerve injury include supracondylar fractures of the humerus and both bones forearm fractures. These types of injuries are serious fractures that often require surgical intervention for treatment. If there is associated damage to the median nerve, this should be evaluated and treated if necessary.

Nerve Contusions

A nerve contusion is a blunt injury to a nerve from a direct blow. Unlike a nerve laceration where there is a direct injury to the nerve causing a separation in the structural anatomy of the nerve, a contusion causes an injury to the nerve without physical separation. The amount of dysfunction and the prognosis for recovery after a nerve contusion is determined by the severity of the injury. A less severe contusion typically results in some transient numbness and tingling in the area where the nerve provides sensation.

More severe contusions, on the other hand, can result in significant nerve dysfunction including weakness and even permanent nerve damage. The duration of symptoms following a nerve contusion will depend on the severity of the injury and can last from a few minutes up to a few months.

Treatment

The most important step in the treatment of any nerve disorder is to ensure there is a clear understanding of the location and the cause of the nerve dysfunction. As described previously, often the location of nerve damage is not at the same location where a patient experiences abnormal symptoms including numbness, tingling, and weakness. Once the specific cause of the nerve dysfunction has been identified, treatments can be appropriately targeted to this area.

When there is ongoing compression or damage occurring to a nerve, the initial goal of treatment should be to relieve this pressure on the nerve.

Sometimes this can be accomplished with simple steps such as splinting or padding around the nerve. When there is more severe compression, a surgical procedure to relieve pressure on the nerve may become necessary. When there is a direct injury or laceration to a nerve, a surgical procedure to repair the continuity of the nerve should be considered. In cases where there is a larger segment of damage to a nerve, it may be necessary to consider nerve grafting to span the area of nerve damage.

People who have more severe nerve injuries or long-standing damage to the nerve may experience incomplete recovery following treatment. Nerve function is notorious for taking long times to recover, and often the recovery is not complete. In more severe injuries, it may take months or even years to determine the amount of recovery that will occur.

People with these types of severe injuries to the median nerve may experience areas of the upper extremity for permanently lack normal sensation, and they may have weakness of the muscles controlled by the median nerve. When muscles do not function as a result of nerve injury, there are surgical procedures that can be considered to compensate for these losses in function.

A Word From Verywell

The median nerve is one of the major nerves that is critical to the normal function of the upper extremity. Careful examination can determine if there are abnormal functions of this median nerve. The most common type of injury to the median nerve is called carpal tunnel syndrome. When the median nerve is not functioning normally, treatments can be targeted to the specific location of dysfunction. However, nerve injuries are notorious for taking a long time to recover. Be sure to discuss any discomfort or pain with your doctor so that if you have sustained a nerve injury, you can treat it as early as possible as early intervention is key.

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